Synthesis and sonophotocatalytic activities of ZnO\BiVO4\Co3O4 composites

The development of multifunctional materials for water pollution remediation using pollen and sporopollenin

Pollen is a promising material for water treatment owing to its renewable nature, abundant sources, and vast reserves. The natural polymer sporopollenin, found within pollen exine, possesses a distinctive layered porous structure, mechanical strength, and stable chemical properties, which can be utilized to prepare sporopollenin exine capsules (SECs). Leveraging these attributes, pollen or SECs can be used to develop water pollution remediation materials. In this review, the structure of pollen is first introduced, followed by the categorization of various methods for extracting SECs. Then, the functional expansion of pollen adsorbents, with an emphasis on their recyclability, reusability, and visual sensing capabilities, as opposed to mere functional group modification, is discussed. Furthermore, the progress made in utilizing pollen as a biological template for synthesizing catalysts is summarized. Intriguingly, pollen can also be engineered into self-propelled micromotors, enhancing its potential application in adsorption and catalysis. Finally, the challenges associated with the application of pollen in water pollution treatment are discussed. These challenges include the selection of environmentally friendly, non-toxic reagents in synthesizing pollen water remediation products and the large-scale application after synthesis. Moreover, the multifunctional synthesis and application of different water remediation products are prospected.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Ultrasound-Assisted Synthesis of a ZnO/BiVO4 S-Scheme Heterojunction Photocatalyst for Degradation of the Reactive Red 141 Dye and Oxytetracycline Antibiotic

The preparation of novel sunlight active photocatalysts for complete removal of pollutants from aqueous solutions is a vital research topic in environmental protection. The present work reports the synthesis of a ZnO/BiVO₄ S-scheme heterojunction photocatalyst for degradation of the reactive red dye and oxytetracycline antibiotic in wastewater. ZnO and BiVO₄ were first fabricated by a hydrothermal technique, and then, the ZnO/BiVO₄ heterostructure was synthesized using an ultrasonic route. An increase of the surface area, compared to that of ZnO, was found in ZnO/BiVO₄. The enhancement of charge separation efficiency at the interface was obtained so that a remarkable enhancement of the photocatalytic performance was detected in the prepared heterojunction photocatalyst. Complete detoxification of harmful pollutants was achieved by using the economical solar energy. The removal of the pollutants follows the first-order reaction with the highest rate constant of 0.107 min^-1. The stability of the prepared photocatalyst was detected after five cycles of use. The ZnO/BiVO₄ S-scheme heterostructure photocatalyst still provides high photoactivity even after five times of use. Hydroxyl radicals play an important role in the removal of the pollutant. This work demonstrates a new route to create the step-scheme heterojunction with high photoactivity for complete removal of the toxic dye and antibiotic in the environment.

Anchoring ZnO on spinel cobalt ferrite for highly synergic sono-photo-catalytic, surfactant-assisted PAH degradation from soil washing solutions

In this study, the photocatalytic activity of ZnO was effectively improved via its combination with spinel cobalt ferrite (SCF) nanoparticles. The catalytic performance of ZnO@SCF (ZSCF) was investigated in coupling with UV irradiation and ultrasound (US), as a heterogeneous sono-photocatalytic process, for the decontamination of phenanthrene (PHE) from contaminated soil. Soil washing tests were conducted in a batch environment, after extraction assisted by using Tween 80. Several characterization techniques such as XRD, FESEM-EDS, BET, TEM, UV-vis DRS, PL and VSM were utilized to determine the features of the as-prepared catalysts. ZSCF showed an excellent catalytic activity toward degradation of PHE in the presence of US and UV with a significant synergic effect. It was found that more than 93% of PHE (35 mg/L) and 87.5% of TOC could be eliminated by the integrated ZSCF/US/UV system under optimum operational conditions (pH: 8.0, ZSCF: 1.5 g/L, UV power: 6.0 W and US power: 70 W) within 90 min of reaction. After five times of use, ZSCF illustrated good reusability in the decontamination of PHE (87%) and TOC (79%). Quenching tests revealed the contribution of h⁺, HO^• and e^- species during PHE degradation over ZSCF/UV/US and an S-scheme photocatalytic mechanisms was proposed for the possible charge transfer routes under the ZSCF system. This study provides the important role of SCF in enhancing the ZnO photocatalytic activity due to its high performance, easy recovery and excellent durability, which it make an efficient and promising catalyst in environmental clean-up applications.

Effect of the Type of Heterostructures on Photostimulated Alteration of the Surface Hydrophilicity: TiO2/BiVO4 vs. ZnO/BiVO4 Planar Heterostructured Coatings

Here, we report the results of comparative studies of the photostimulated hydrophilic behavior of heterostructured TiO2/BiVO4 and ZnO/BiVO4, and monocomponent TiO2 and ZnO nanocoating surfaces. The chemical composition and morphology of the synthesized nanocoatings were characterized by XPS, SEM, and AFM methods. The electronic energy structure of the heterostructure components (band gap, top of the valence band, bottom of the conduction band, and Fermi level position) was determined on the basis of experimental results obtained by XPS, UV-V absorption spectroscopy and Kelvin probe methods. According to their electronic energy structure, the ZnO/BiVO4 and TiO2/BiVO4 heterostructures correspond to type I and type II heterostructures, respectively. The difference in the type of heterostructures causes the difference in the charge transfer behavior at heterojunctions: the type II TiO2/BiVO4 heterostructure favors and the type I ZnO/BiVO4 heterostructure prevents the photogenerated hole transfer from BiVO4 to the outer layer of the corresponding metal oxide. The results of the comparative studies show that the interaction of the photogenerated holes with surface hydroxy-hydrated multilayers is responsible for the superhydrophilic surface conversion accompanying the increase of the surface free energy and work function. The formation of the type II heterostructure leads to the spectral sensitization of the photostimulated surface superhydrophilic conversion.